This invention relates to a pole piece design to generate very homogeneous magnetic field even with an asymmetric, open C-arm magnet to be used in medical magnetic resonance imaging equipment or MRI equipment.
In magnetic imagers with pole pieces it has been quite expensive to generate homogeneous magnetic flux inside a large enough imaging volume. It has normally required very symmetric structure for the magnet. U.S. Pat. No. 4,672,346 describes this kind of symmetric structures for a permanent magnet imager where the realization of homogeneity requires the movement of very large masses, at least the movement of the whole pole piece. U.S. Pat. No. 5,003,276 describes this kind of symmetric structure wherein a complex mechanism for shimming is done with tens of movable tuning pieces attached to both pole pieces. The inhomogeneity of an asymmetric structure is essentially larger than that of a symmetric structure and no working solution has been presented to achieve the required homogeneity of 20 ppm.